A Quantitative Genetic Test of Adaptive Decoupling Across Metamorphosis for Locomotor and Life-History Traits in the Pacific Tree Frog, Hyla Regilla

Abstract

Abstract. Metamorphosis is assumed to be beneficial because it can break developmental links between traits in the different phases of a complex life-cycle and thereby allow larval and adult phases to adapt independently. I tested the prediction that correlations between the larval and adult phases are smaller than within stages. I estimated phenotypic and additive genetic variances and correlations for tadpole swimming speed, frog jump distance, body size, and larval period in a single population of the Pacific tree frog, Hyla regilla. These traits are known or reasonably assumed to be important for survival in this and other anuran species from temporary ponds. Only the three size variables were affected by sire identity. Heritabilities for locomotor performance, larval period, and size-independent performance were low (0.00-0.23) and not significant. Body size measurements showed somewhat higher and statistically significant heritabilities (0.24-0.34). Most traits were phenotypically correlated. On average, phenotypic correlations were larger between phases than within phases (0.41 vs. 0.28). Genetic correlations involving body-size traits were positive and large, and average within-and between-phase genetic correlation coefficients were identical (0.81). These results do not support the adaptive decoupling hypothesis, and they indicate that a paucity of additive genetic variation is a likely constraint on the evolution of traits measured for this population.

Trait Performance Correlations across Life Stages under Environmental Stress Conditions in the Common Frog, Rana temporaria

“…Our results contrast with those of Watkins [5], who did find a correlation between tadpole and froglet performance. However, it should be noted that in Watkins's [5] study this correlation disappeared after controlling for body size. Hence our interpretation of both his and our results, is that performances in the juvenile and froglet stages are decoupled, but that jumping ability is affected by the size of the froglet, which is carried over from the size of the tadpole.…”

“…Therefore, undergoing metamorphosis does not represent a completely new start for froglets; instead the performance of the individual is still constrained by the burden of its developmental past, as discussed by Releya and Hoverman [36]. Our results contrast with those of Watkins [5], who did find a correlation between tadpole and froglet performance. However, it should be noted that in Watkins's [5] study this correlation disappeared after controlling for body size.…”

“…A logistic regression confirmed that survival did not differ among populations (Z = −1.3, P = 0.2) or treatments (Z = 1.9, P = 0.06), although the treatment effect was only marginally non-significant and slightly more individuals died where water levels were kept constant (53%) compared to treatments with falling water levels (40%). The mortality figures are within the ranges reported in other studies where frogs have been raised from the egg stage until Gosner stages 45–46 with complete resorption of the tail [5], [6], [15].…”

“…While several studies have examined the relationship between morphological traits across life stages in frogs e.g. [3], [4], [5], [6], [7], few have examined how behavioural traits are coupled across the different stages. In the present study we focus on how morphology and locomotor behaviour is correlated across life stages.…”

Do traits separated by metamorphosis evolve independently? Concepts and methods

“…The situation is reversed in Pacific tree frogs as genetic correlations for locomotory traits are positive between the larval and the adult stage [29]. On the other hand, some traits that seemed to have similar functions at different life stages were found to be genetically independent.…”